MIT, Vienna university develop 'optical transistors'

The future of optical computing has gotten brighter, as separate announcements by MIT and an Austrian university each claim breakthroughs in “optical transistors”.

Researchers at the Vienna University of Technology said recently that they’ve been able to achieve a key step on the road to building an optical transistor, which could be the foundation of an optical computer some day. Back on this side of the Atlantic, at MIT, researchers have built an optical switch that can be tuned by a single photon.

Researchers have hoped to replace electron-based silicon transistors for years for several reasons, not the least of which is managing the power consumption used by computers and the chips that power them. Electrical transistors produce waste heat, which can build up in a computer and damage the chip itself unless properly cooled.

To date, optics have been used as the foundation of high-speed communication networks to transmit massive amounts of data across short distances.Companies like Intel have managed to use optical cables to connect boards within servers, but optics-based chips have largely remained lab experiments, with companies like IBM working to further the technology.

That’s the goal of both the MIT and the TU Vienna researchers, which detailed their work in recent academic papers.

Specifically, the TU Vienna researchers said that they’ve been able to adjust the polarization of light via an electrical current, which would create the ones and zeroes that form the foundation of the binary nomenclature that underlies computing. Moreover, the researchers achieved this using light at one terahertz frequencies, potentially allowing those computers to operate at about 250 times the speed of the fastest 4-GHz chips today.

”This is the very principle of a transistor,” said Prof. Andrei Pimenov, in a statement released by the Institute of Solid State Physics of TU Vienna. “The application of an external voltage determines whether current flows or not, and in our case, the voltage determines whether the light arrives or not.”

As with any research, however, significant hurdles need to be overcome. For instance, a press release issued by the TU Vienna researchers indicated that “beams of light” were being manipulated, and apparently not light passing through optical fibers. In a conventional chip powered by electrons, those electrons move through literally billions of transistors, all etched into silicon—not just one. Furthermore, the polarization of the light was only achieved by manipulating it as it passed through a “special material”. Two years ago, that special material was mercury telluride platelets, and an electrical coil was required. Now, the researchers say that they’ve reduced the power to less than a single volt—a significant improvement, granted.

The researchers also noted that changing the polarization of light without a large part of it being lost is difficult, but failed to say how much (if any) is being lost by their method.

MIT uses light to control light

MIT researchers took a different approach, developing an experimental optical switch that could be controlled via a single photon—using light to control light, versus using electricity to control light, as the Viennese researchers did.

What MIT did was to design a pair of mirrors that were transparent to a given wavelength of light when “on,” allowing light to pass through. When “off,” the mirrors should have blocked the photons, but they didn’t. About 20 percent of the light passed through. By filling the space between the mirrors with supercooled cesium atoms, the light was blocked entirely.

MIT also believes that a more fruitful avenue of research would be to use quantum computing, where particles in a “superposition” state could be both on or off at the same time, allowing operations to be run in parallel.

“It’s exactly the same story, except that instead of using these ultracold atoms in the cavity, you use a microscopic cavity on a semiconductor chip on a semiconductor and you use a quantum dot grown inside of the semiconductor as an artificial atom,” said Jelena Vuckovic, a professor of electrical engineering at Stanford University cited by MIT. “There would be extra steps that people would have to take in order to implement the right energy-level structure. But in principle, the physics could be translated to a platform that could be cascaded and more easily integrated.”

Quantum computing, however, is an entirely different field, one that is still not wholly understood. D-Wave Systems has built what it calls the first quantum computer, one of which has been bought by Google and installed in a Quantum Artificial Intelligence Lab it built with the cooperation with NASA’s Ames Research Center. But the D-Wave Two, the company’s latest “qubit processor,” is housed inside a cryogenics system within a 10 square meter shielded room.